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Chapter 3 Meshing Methods for 3D Geometries

Chapter 3 Meshing Methods for 3D Geometries. ANSYS Meshing Application Introduction. Overview. Geometry Requirements Meshing Methods Tetrahedrons Patch Conforming Patch Independent (ICEM CFD Tetra) Swept Mesh Automatic MultiZone CFX-Mesh Workshop 3.1

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Chapter 3 Meshing Methods for 3D Geometries

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  1. Chapter 3Meshing Methods for 3D Geometries ANSYS MeshingApplication Introduction

  2. Overview • Geometry Requirements • Meshing Methods • Tetrahedrons • Patch Conforming • Patch Independent (ICEM CFD Tetra) • Swept Mesh • Automatic • MultiZone • CFX-Mesh • Workshop 3.1 • Combining Sweep and Tetrahedral Methods for a Multibody Part • Inflating Tetrahedral and Sweep Methods

  3. Geometry Requirements • All the 3D meshing methods require that the geometryconsist of solid bodies • If an imported geometry consists of surface bodies,additional steps would be required to convert it to a3D solid if a 3D mesh is to be generated in the ANSYS Meshing Application (although surface bodies can be meshed with surface meshing algorithms)

  4. Tetrahedral Meshes • Advantages • An arbitrary volume can always be filled with tetrahedra • Can be generated quickly, automatically, and for complicated geometry • Can be easily combined with curvature and proximitysize functions to automatically refine the mesh in critical regions • Can be combined with inflation to refine the mesh near solid walls (boundary layer resolution) • Disadvantages • Element and node counts are higher than for a hex mesh with a similar mesh density • Generally not possible to align the cells with a flow direction • Not well suited for thin solids or annuli due to non-isotropyof geometry and nature of element

  5. Tetrahedral Algorithms • Two different algorithms are available for generating tetrahedral meshes in the ANSYS Meshing Platform • Patch Conforming: A surface mesh is generated first using a Delaunay or Advancing Front surface mesher which will, by default, respect all faces and edges in the geometry (note: some built-in defeaturing for features below the minimum size limit). The volume mesh is then created from the surface mesh via an algorithm based on TGRID Tetra. • Patch Independent: Here a volume mesh is generated and projected tosurfaces to yield the surface mesh. Faces and edges will not necessarily be respected unless loads or boundary conditions are scoped to them.This method is more tolerant of poor quality CAD. The patch independent algorithm is based on ICEM CFD Tetra. • Both tetrahedral algorithms can be inflated for boundary layer resolution often required for CFD

  6. Tetrahedral Meshing Common Parameters Minimum and Maximum Sizes Face and Body Sizes Advanced Size Functions (Curvature and/or Proximity) Growth Rate (gradual variation for CFD, avoid sudden jumps) Smoothing (helps achieve a more uniformly sized mesh) Statistics Mesh Metrics

  7. Patch Conforming Tetrahedrons • Right click on Mesh, inserta Method and Choose the bodies to which to apply the method. • Set the Method to Tetrahedrons andthe Algorithm to Patch Conforming • Different parts can have differentmethods. A single part with multiple bodies can include a mix of patch conforming tetrahedrons and sweep methods and will still produce a conformal mesh (Workshop 3.1) • The Patch Conforming method canbe used in conjunction with PinchControls to help remove short edges. It also has built-in mesh defeaturing based on the minimum size Small Hole Faces inClose Proximity

  8. Patch Conforming Tetrahedrons Example Resolution ofCircular Hole Faces (and edges) are respected

  9. Patch Independent Tetrahedrons • Useful for CAD with many surface patches, sliver faces, short edges, poor surface parameterization, etc. • With the Method to Tetrahedrons, setthe Algorithm to Patch Independent • Faces and edges will not necessarily be respected unless a load or namedselection is scoped to them • Note that there are additionalsettings concerning defeaturing aswell as settings for curvature and proximity Small Hole Faces inClose Proximity

  10. Patch Independent Tetrahedrons No Named Selections: Faces and Edges are not respected

  11. Patch Independent Tetrahedrons Named Selections: Faces and Edges are respected

  12. Inflating the Tetrahedral Method • Inflation is scoped to bodies and defined for faces

  13. Sweep Method Body must be sweepable Inflation can yield pure hex or prisms Manual or automatic source/target Normally single source to singletarget face, automatic thin model can be used for multiple faces with multipleelements through the thickness Right-click on Mesh: Show Sweepable Bodies

  14. Sweep Method: Source/Target, Mesh Type

  15. Sweep Method: Thin Model • Useful when there are multiple faces as inthe geometry shown below which has 3source and target faces 1 2 3

  16. Sweep Example with Bias in Sweep Direction • Geometry with a single source and target face can be swept with abias in the sweep direction 1 (Faces have been merged either in CAD or with VT)

  17. Sweep with Inflation • Inflation is scoped to a face withinflation specified on edges 1 (Faces have been merged either in CAD or with VT) • Thin Model Sweeps cannot be inflated

  18. Automatic Method The Automatic setting toggles between Tetrahedral (Patch Conforming) and Swept Meshing, depending upon whether the body is sweepable. Bodies in the same part will have a conformal mesh. Tetrahedron (Patch Conforming) Swept Tetrahedron (Patch Conforming) Programmed Controlled Inflation No inflation

  19. MultiZone Sweep Meshing • Based on ICEM CFD Hexa Blocking • Automatic geometry decomposition • With the swept method, this part would have to be sliced into 3 bodies to get a pure hex mesh With MultiZone, it can be meshed directly!

  20. MultiZone for Pipe Intersection 2 1 3 4

  21. MultiZone for Pipe Intersection • Free block in center (here meshed with tets)

  22. Adding Inflation to MultiZone • As for the tetrahedral meshers, inflation is scoped to bodies anddefined for faces

  23. MultiZone Mesh with Inflation

  24. CFX-Mesh Method Tet/prism mesher or extruded meshes for geometries with a periodic translation or rotation CFX-Mesh uses a ‘loose’ integration Selecting Right Mouse ‘Edit…’ on the Method launches CFX-Mesh as a separate window that isdifferent than the WorkbenchMeshing environment. No Meshing Application sizings are respected or transferred to CFX-Mesh

  25. Workshop 3.1 Static Mixer with Patch Conforming Tetrahedronsand Sweep Methods

  26. Goals This workshop will illustrate combining the Patch Conforming Tetrahedrons and Sweep Methods for a multibody part to yield a conformal mesh with hybrid tet/prism and hex elements The use of Inflation is also demonstrated for both the Sweepand Patch Conforming methods

  27. Specifying Geometry Copy the sm.agdb file from the tutorial files folder to your working directory Start Workbench and double-click the Mesh entry in the Component Systems panel at the right Right-click on Geometry in the Mesh entry in the Project Schematic and select Import Geometry/Browse Browse to the sm.agdb file you copied and click Open Note that the Geometry entry in the Project Schematic now has a green check mark indicating that geometry has been specified The first 9 steps repeatthe process followed forTutorial 2.1.

  28. Initial Mesh • Double-click the Mesh entry in the schematic or right-click and select Edit • Expand the Geometry entry in the Outline and note that there is a single part with 4 bodies • Left click on the Mesh entry and set the Physics preference to CFD and select the FLUENT solver • Right click on Mesh and Insert a Mesh Method. Select the three cylindrical bodies from the Model View and choose the Sweep Method • Set the Src/Target Selection to Manual Source and select the three end faces of the cylindrical bodies 1 2 3

  29. Patch Conforming Tetrahedrons • Right click on Mesh and Insert a Mesh Method. Select the central conical bodies from the Model View and choose the Tetrahedrons Method with the PatchConforming Algorithm

  30. Initial Mesh (no Inflation) • Expand the Inflation entry in the Mesh settings and set the Use Automatic tet Inflation option to None as you will manually inflate the two different methodsMake sure the mesh settings are as shown at right • Right-click on Mesh and generate the mesh. Notice that the mesh is conformal

  31. Inflating the Sweep Method • Right-click on the Sweep Method and choose Inflate this Method. The inflation will be scoped to the three source faces • For the boundary, you will need to select the three outer circular edges of the faces (you may need to enable the Select Edges toggle to simplify this). • Set the maximum thickness to 0.2 m, leaving the other settings at defaults. Right-click

  32. Inflating the Tetrahedrons Method • Right-click on the Tetrahedrons Method and choose Inflate this Method. The inflation will be scoped to the central body. Select the 2 outer radial faces of the conical body • Set the Inflation Option to Total Thickness and set the Maximum Thickness to 0.2 m, leaving the other settings at defaults. Right-click

  33. Generating the Mesh • Generate the mesh. Note that the swept regions still produce hexes while the central body produces prisms and tetrahedrons. • Verify that all meshes are conformal and save your project.

  34. Interior View of Inflated Mesh

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